<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script>
			var month = 30;
			if (month <1 || month > 12) {
				month = Number.NaN;
			}
			console.log(month);//NaN
		</script>
	</head>
	<body>
	</body>
</html>
